Multiplex pulse transmission system



NOV. 17, 1953 Q X, N, POTER 2,659,768

MULTIPLEX PULSE TRANSMISSION SYSTEM Filed Feb. l, 1951 3 Sheets-Sheet l G. x. N. P01-IER 2,659,768

MULTIPLEX PULSE TRANSMISSION SYSTEM 3 Sheets-Sheet 2 Filed Feb. l, 1951 Hg. s

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Nov. 17. 1953 G, x N. POTlER 2,659,768

MULTIPLEX PULSE TRANSMISSION SYSTEM Filed Feb. l. 1951 3 Sheets-Sheet .'5

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ll ll u Patented Nov. 17, 1953 UNITED STATES PATENT OFFICE 1 Claim.

The object of the present invention is an improved method of multiple channel electrical communication by means of interleaved or inter-- mingled recurrent electric pulse trains, based on the principle of division in time and the type of modulation called pulse position modulation without iixed time reference.

More specifically, the object of the method according to the invention is the provision of multiplex systems in which intelligence corresponding to the various communication channels is represented by the time intervals between recurrent of successive pulses, none of which has a iixed time position with respect to fixed periodic reference instants. Such a type of transmission is sometimes called a multiplex pulse interval system.

It is known that in various methods for multiplex transmission by means of recurrent pulses, the total transmission time is supposed to be divided into equal time intervals of a duration T, themselves subdivided into equal and shorter elementary time intervals T/ (N+ l), N being the number of communication channels and an (PH-Um elemental time interval being reserved for a synchronization signal (often called a pilot signal), not subjected to any modulation and which is given a particular shape, allowing it to be easily identified by the receiving apparatus and used for the synchronization thereof. It is not indispensable that all the time intervals reserved for each channel be equal, but this arrangement is generally adopted as being simpler in practice.

In such systems, inside each channel time interval. pulse is generated, the position of which be varied in time, as a function of the instantaneous amplitude of the corresponding channel modulation signal. It should be understood that by time position of a pulse is meant the time interval existing between a reference instant fixed with respect to the ends of the duration of the time interval assigned to one channel and the time when this pulse is generated if it is of very short duration. If the pulse has an appreciable duration, the instant of its beginning will serve for defining its position in time. designated hereinafter more briefly as the position All the pulses transmitted within the time T will be called a pulse group. A pulse train will be the whole of the pulses corresponding to one given channel.

Such multiplex transmission methods oiier numerous advantages, but, however, they offer the drawback that in the case of a system with a very large number of channels they do not benet from the statistical advantage existing in carrier current multiplex systems using an amplitnde or frequency modulation, as each elementary time interval assigned to one channel remains absolutely inactive if, at a given instant, no modulation signal is present on said channel.

The statistical effect just mentioned has been particularly studied in a paper by B. D. Holbrook and J. T. Dixon entitled Load rating theory for multi-channel amplifiers," published in the Bell System Technical Journal for October 1939, volume XVIII, pages E24 to 644. The results of this wort: are numerical data on the importance of said statistical effect. It may be noted that in the case of a telephone transmission, the peak value of the signal is seldom reached and that, in case it is limited by clipping in such a manner that the clipping level be reached during 1% of the time, there will be during 99% of the time an instantaneous level at most equal to one quarter of the clipping level. In such a pulse system using position modulation, this amounts to saying that three quarters of the duration of the time interval assigned to each channel are generally unused. In a system including a large number of channels. in which account must be taken of the fact that the modulations of the various channels do not add up arithmetically, but according to the laws of probability, this effect is still more pronounced.

To take advantage of this statistical effect, therefore, systems have been proposed, in which the duration of an elementary time interval is reserved for a channel pulse only during the time when this total duration is eiiectively utilized, which allows, during the complementary time, to move the next pulse closer thereto.

In a system utilizing such an arrangement it would be possible to increase the number of communication channels transmitted with respect to what exists in conventional systems, or, on the contrary, for a xed number of channels, to increase the value of the displacement of the position of one channel` pulse and, consequently. the signal to noise ratio.

.Yhe above mentioned possibility has already been taken advantage of in certain multiplex transmission systems proposed. Such a system has already been described in the `French Patent No. 946,345 of April 26, 1947, in the name of P. F. M. Gloess, in which the instantaneous position of a channel pulse is aiiected by all the modulations from a number of other channels and in the prior U. S. patent application Serial No. 83,302, filed March 25, 1949, in the names of P. F. M. Gloess and L. J. Libois, which concerne a modification in which the modulation applied to each pulse includes the normal alternoting telephone signal to which a D. C. component has been added, proportional to the amplitude of said signal as proposed in the French Patent No. 870,474 of February 28, 1941, in the name of the corporation Le Materie-l Telephonique" for electrical switching, and.. signalling systems.

The various systems thus proposed offer the common characteristic that, while in the absence of any modulation, the N communication pulses of an N-channel system are grouped in the vicinity of one end of the titre interval Treserved for a pulse group and then occupy only a small portion of this time interval, ther position modulations of the pulses of the various channels have an additive character. For instance, if it is assumed that, in the absence of any modulation, all the communication pulses are grouped in the vicinity of the pilot pulse, at the beginning oi the time interval T, the modulation of the first channel will have the effect of displacing the instantaneous position of the corresponding pulse with respect to the pilot pulse, the modulation of the second channel will have the effect of displacing the position of the corresponding pulse, by an amount proportional to this modulation, with respect to the instantaneous position of the pulse corresponding to the flrst channel, and so on.

Brienyn the modulation of a given channel is represented in proportion by the time interval between the pulse corresponding to this channel and the previous pulse, the latter being merely the pilot pulse in the case of the first channel (see Telemetering from V-Z rockets, by V. L. Heeren et al., Electronics, March 1947, page 100, particularly Figure 4). It will be imagined that, owing to the above mentioned statistical effect, it is then possible to give each pulse, for the ,same modulation signal, a larger ,displacement in position than would be the case if said pulse had to remain always inside a time interval invariably assigned to the corresponding channel.

In the various pulse transmission systems util Vizing this type of additive modulation, it has been found advantageous, further, when the modulation to be transmitted is a telephone sienai or the like, of an essentially alternating character, to add to it a D. C. component substantially proportional to the instantaneous amplitude of the signal. This arrangement offers the advantage that the modulation signals then talee on a unipolar character, the corresponding position displacements of the pulses being of a variable magnitude but occurring always in the same direction. It will be easily understood that this is a necessary condition if it is desired to take advantage of the statistical effect for both the positive and negative semi-periods of the telephone signal.

The various known methods for putting into practice this type of pulse transmission offer, however, certain ditlculties for their realization, especially for signal demodulation by the receiving apparatus.

An object of the present invention is a transmission method (sending and receiving), making it possible to obviate these difliculties.

The method which is ,an object of the present invention is, at the same time, a particular sending method making it possible to realize in a simple manner the above described type of transmission, and a receiving method making it possible to restore the modulation signals originally applied to the various communication channels, owing to a particular selecting device, taking' into account the fact that the elementary time inter vals assigned to each pulse train, in this transmission systcm, have no fixed positions with rcspect to the synchronization. pulses or with relspect to predetermined refer-snee instants.

, Thev method according.. to .the .invention consists, in a characteristic manner,V at the sendingr end, in measuring, at instants oquidistant in time, at the frequency of the pulso groups, the instantaneous amplitude of each one ol` the modulation signals to `be transmitted, in storingthe ampln Atudes thus measured for a certain time, prefer ably equal to the duration of one pulse group. in usingthestored amplitude corresponding to the first communication channel for defining a time interval counted from the pilot pulse or from a reference instant fixed with respect to said pilot pulse and proportional to the stored amplitude corresponding to the first communication channel, a rst communication pulse correspondingl to said rst channel being sent at the end of :said time interval, in using this iirst pulse and the stored. amplitude corresponding to the second channel for defining a second time interval counted from said first pulse and proportional to said stored amplitude corresponding to the second channel, second communication pulse beine sent at the end of second time interval, in operating in the same manner until all channels and all pulses are exhausted, and in staggering' in time the various pulse sendings in such a manner that, even in the absence oi any modulation, two different pulses can never coincide in time.

Alternately, it is possible, according to a modification of the method of the invention, to dis-- tribute in time the various communication pulses by means of successive partial delays introduced after the generation of each one of said pulses after it has received its final position module ou and beforel it is utilized for dcning the instant taken as an origin for the time interval proportional to the modulation of the next channel.

It is this modification of the method accor-iing to the invention which is made use of in the embodiment described hereinafter.

At the receiving end, the method consists in rst separating by any known means, the pilot pulse from the other pulses, in using said pilot pulse for the generation of auxiliary puises at a constant frequency equal to that of the pulse groups, in measuring the successive time intervals separating the pulses and in deriving therefrom electrical values proportional to said time intervals, which are collected in distinct circuits equal in number to said time intervals, and consequently to that of the communication channels, in storing for a certain time these electrical values and in utilizing them for modulating in amplitude (or in duration) and proportionally to said values the auxiliary pulses ol constant fre-- quency, in demodulating said auxiliary pulses by known means for obtaining signals proportional to the original modulation signals and in direct- Ving the demodulation products obtained toward utilization circuits.

With the usual modulation methods for realising the same type oi transmission, crosstalk is introduced in each. communication channel by the fact that the time separating two consecutive analyses of the modulating signal at the sendingr end and two consecutive restitutions of this same modulating signal at the receiving end is not constant.

An advantage of the method which is an object of the invention lies in the fact that the time separating two consecutive analyses or two restitutions of the same channel modulating signal is constant, although the time separating two consecutive pulses corresponding to this same channel is variable according to the very principle of transmission adopted.

The use of a common principle for measuring and storing, both at the sending and receiving ends, makes it possible, in the method according to the invention, to restore to the instantaneous amplitudes derived from the modulation signal the suitable equidistance, both at the receiving and sending ends. It is then always possible, whatever the number of channels, to make a maximum use of the time reserved for each pulse train either for improving the signal to noise ratio or for decreasing the bandwidth necessary for transmission.

The above-described method necessitates the use of complementary transmitting and receiving equipment in a communication system for carrying out the said method, as it is obvious that otherwise undesirable and possibly prohibitive cross-talk and distortion would occur, due to lack of proper synchronization between the sampling of modulation signals at the transmitting end and their restitution at the receiving end.

A particular embodiment of such a communication system will now be described by way of example without in any way limiting the scope of the method which is the object of the invention. It will be obvious to any expert in the art that in particular the storing device hereinafter described could be replaced by various known devices, such as storage electronic tunes, for instance. Other elements involved, such as modulators, generators, synchronizing devices and demodulators may in practice be of any suitable design.

Other features and objects of the invention will be better understood from the following description with reference to the appended drawings, wherein:

Figure l shows, schematically, one type of embodiment of the device for applying the method of the invention;

Figure 2 shows the diagram, as a function of time, of a modulation signal, such as it usually exists, for instance in a telephone circuit;

Figure 3 shows the diagram, as a function of time, oi a modulation signal with a superposed D. C. component, such as it is proposed to use in the method of the invention;

Figure e shows, in line A, the time positions, with respect to the ends of a time interval of a duration equal to that oi a pulse group, of the pilot pulse, distinguished cy its larger amplitude. and oi channel pulses, in case there is momentarily no modulation signal on any communication channel, while the same figure, in line B, represents the time positions ci the same pulses when modulation signals are present on the communication. channels;

Figure 5 shows, schematically, a measuring and storing device involved in the transmission system of Figure .l and capable of measuring and soring the amplitude of a modulation signal or the time interval between two pulses; and

Figure is a diagram ci the electrical voltages existing at various points of the transmission system.

For greater simplicity, it has been assumed, in the following description and in the figures. that the transmission system described comprises only three communication channels and that the modulation signals are telephone signals, but it should be clearly understood that the invention may be app-lied, just as well, to systems comprising a much larger number of communication channels or to the transmission oi other types oi communication signals.

The operation of the device of Figure l may be explained as follows:

The modulation signals from the three communication channels are respectively applied at lill, |02, |03 to three D. C. restorers |04, |65, |65 adding to them, by well known means, the D. C. component necessary to make them unipolai` and to transform their wave shape from that of Figure 2 to that of Figure 3. Upon their issuing from |04, |05, |06, the modified signals thus obtained are respectively applied to one of the inputs of three measuring` and storing devices |01, Iil, |69, the operation of which will subsequently be explained in detail. These measuring and storing devices are also energized by two series of periodic pulses from a generator of pulses oi short duration Ill), which generates them with the period T of the pulse groups, i. e. at the pilot pulse frequency. The pulses from Ilil are applied, through a delay network to a second input of each one of the measuring and storing devices |01, |88 and |09 and, on the other hand, directly to a third input thereof, for the purpose of setting them at rest at the end oi each working period T. The function of the measuring and storing devices is to measure and store,

`- for a certain time, slightly less than the duration of one pulse group, the instantaneous amplitude of the modified modulation signals applied to one of their inputs at IM, l, |66. The stored instantaneous amplitudes appear in the form oi electrical voltages at the outputs of lill, |58. |09 and are applied to pulse position modulators of the conventional type, H2, |I3, H4. The delay obtained with the network il! being small in value and being only for the purpose of separating sharply the instant at which the signals from |04, |05, |06 are measured from that at which the pilot pulse is generated, electrical voltages with values proportional to the stored amplitudes of the respective modulation signals are present at the outputs of |01, |08, 09 during almost the whole duration T of each pulse group. These electrical voltages will be called hereinafter stored modulation signals.

The function of the position modulators H2, I3, M is to delay, by an amount proportional to the stored modulation signals which ere respectively applied to one of their inputs, the time or time position of the pulses which are applied at their other input. The principle and operation of such position modulators are well known in the pulse technique. It is known that position modulated pulses are generally obtained by a diierentiation of duration modulated pulses and numerous methods of duration modulation are known at present and may be utilized here. One may mention, for instance, the one described in the French Patent No. 912,617, of July 20, 1945, in the name of Patelhold Patentverwertungs 8; Elektroholding A. G.

In Figure l, the position modulator |12 corresponding to the rst communication channel, is thus energized on the one hand by the stored modulation signal from |01, and on the other hand by a delayed pulse, by means of the delay network Ill, with respect to the pilot pulse, by

an amount greater than the delay (itself given by a portion of the network III) of the analysis pulse applied to the second input of |01 with respect to the pilot pulse, in order that the position modulation may be effected in the modulator ||2 only after the end of the measurement in the measuring rnd storing device |01.

The result, at the output of ||2, is the production of a communication pulse which is directed on the one hand toward the mixer H1, the function of which will become apparent further on, and, on the other hand, after being slightly delayed by a delay network H5, toward one of the inputs of the position modulator H3, at the other input of which is applied the stored modulation signal from IES, rnd corresponding to the second communication channel. There is thus obtained, at the output from H3, a second communication pulse delayed with respect to the rst one by an amount proportional to the amplitude stored by |98. This second pulse, in turn, is directed toward ||1 and after beingr slightly delayed by a delay network IIB, is utilized with respect to the third position modulator H4 like the rst one with respect to I I3.

All these pulses are applied to a mixer Ill, which, as will be seen on Figure l, comprises four inputs, corresponding respectively to the pilot pulse and to the communication pulses, and one output. This mixer is a simple device which makes it possible to apply to one output circuit signals from several input circuits. 'The need for the delay networks H5 and H5 is due to the fact that in case of momentarily zero modulation signals on one or more communication channels, i

the possibility of two or more pulses coinciding in time must be avoided.

In prrctice, the delay networks lili and Iii? may often be dispensed with, as a slight delay already exists in most known types of modulator. An alternative method for precluding the possibility of two pulses coinciding in time in case oi zero modulation of one channel would be to add to each modified modulation signal a small and permanent direct-current component.

The pulse group from Ill is then directed towrrd the transmission channel H8 and transmitted by any known means to the receiving end thereof.

At the receiving end, the group ol pulses is first applied in parallel to two pieces of apparatus, the rst one of which, I I9, is a pilot pulse selector for ensuring the production of local synchronization pulses of period T, and that of auxiliary pulses of the same period, the function of which will be .f f

explained later. The second apparatus is a pulse selector |253. of the so-called counter type, which has as many outputs as there are communication channels, and delivers, at its nm output, a pulse of constant amplitude having a duration equal to the time interval bcfvecn the fir-l l il and the nih communication pulse.

Such an apparatus comprises as many electronic dip-flop circuits as there are communication channels, each one of these flip-flop circuits connected with one of the outputs of the appcratus. It also has two inputs. The pilot pulse and the communication channel pulses are applied simultaneously to all nip-flop circuits at the irst input to the apparatus. A special pulse, called an initial condition restoring pulse, which is merely the pilot pulse from ||9 delayed by the delay network |25 is applied, through the second input to the apparatus, to the first flipflop stage.

I of channels there could also be used,

The initial condition restoring pulse sets the first ip-iiop circuit working The pilot pulse and communication channel pulses set at rest the flip-flop circuit which is working Further. a so-called interstage pulse is sent by the nip-nop circuit which is set at rest to the next flip-flop circuit through an interstag'e connection, and sets the latter working There is no inter-stage connection, however, betwen the first and last flip-flop circuits of the lapparatus.

the third fiip-flop working There is obtained,

at the second output of the apparatus, a constant amplitude pulse the duration of which is equal to the time intervrl separating the first communication channel pulse from the second communication channel pulse. The operation is continued in a similar manner for the other dip-flops. However, when the nih (or last) communication chan.- nel pulse sets the nih (or last) flip-flop at rest, no interstage pulse is sent to the first flip-flop which will have to wait for the arrival of the initial condition restoring pulse to pass to the working condition.

The counter selectors such as |29 are described, for instance, under the designation of trigger stages having interconnections to give broken ring action, in a paper by Lawrence Lee Rauch entitled Electronic commutation for telemetering," published in Electronics for February 1947.

In the case of a system with a small number for IEEE, a selector the operation based on the shape of the communication pulses which could receive, in correlation with their sending, different shape according to their rank.

The signals issued from the various outputs of the counting selector |20 are thereafter respectively directed, according to the rank of the channel they represent, toward one of the corresponding measuring and storing devices |22, |23, |211. rwhich are similar to |01, IDS, |09 used in the sending equipment and to the second inout of which said signals are applied, no signal being in this case applied to their first input.

The second inputs of |22, |23, |24 are thus energized by signals from the outputs of |29. The duration of the pulses from one of these outputs is equal to the time separating the pulse of the channel corresponding to said output from the pulse which immediately precedes it and. consequently, to the instantaneous value of thc modulation signal corresponding to this channel. The measuring and storing devices |22, |23. |251, thus measure and store, in the shape of electrical voltages appearing at their outputs, values proportional to the duration of the pulses from the output of |20, to which they are connected, anni consequently to the instantaneous amplitude of the corresponding modulation signal.

The measuring and storing devices |22, |23, |24

pulse.

9 are periodically set at rest by the pilot pulse applied to their third input and slightly delayed by the delay network |25, the function of which is to avoid the setting at rest of the measuringr and storing devices before their output voltage has been utilized by the following apparatus energized by auxiliary pulses derived from the pilot The output voltages from |22, |23, |26 are then applied respectively to the inputs of amplitude or eventually duration modulators |2ii, |21, |22, energized, on the other hand, by periodic auxiliary pulses derived from the pilot pulse .from H9. The signals obtained at the output from |26, |21, |23 are thus modulated proportionally to the original modulation signals and can thon be applied respectively to the amplitude demodu lators (or duration demcdulators) |29. 30, 53|, whence, after demodulation, they are directed towards utilization circuits i32, |33, i3d.

The operation ci a measuring an scoring :lea/ico will be bzter understood by referring to Figure 5 which shows this apparatus schematically, and to the diagram of Figure 5 `which shows the time variation of the electrical voltages existing at various points in the transmission system.

As already mentioned, the measuring and storing device, the diagram of which is given in Fgure 5, is an apparatus comprising three inputs and one output and which, when a time variable electrical voltage is applied to its first input and a control pulse to its second input, causes the appearance, at its output terminals, of a voltage proportional to the value of said time variable vo'tage at the time of application of the control pulse. This voltage at the output terminals of the apparatus is stored until the time of apparition of a rest setting pulse applied to the third input to the apparatus.

The measuring and storing device comprises essentially o pcntcde tube Ecl, a diode 5GB and a triode 5ll3 The Erst input to the apparatus is comprised of the terminal 526, connected through the condenser co5 to the suppressor grid of 50i, the second input of the terminal 5535 connected through the condenser ii to the control grid of 50i. The third input is the terminal 50S con nected through the condenser 50?, to the grid of the triode 563. The suppressor grid of dill and the grid of 5133 are respectively connected through resistances Elfi, 5|! to the negative terminal 5|L of a D. C. high voltage source Ei energizing the whole. The control grid of 5t! is connected through a resistance Elfi to the cathode of the same tube. The voltages applied to the various inputs are applied respectif-.rely between 504, and Ellil on one hand and 5|2 on the other hand,

The cathode of 5cl is connected to 5|2 through a resistance 5|5 in parallel with a de-coupling condenser EN and also, through a resistance 5H to the positive terminal of 5|3, so as to give this cathode a suitable permanent bias. The screen of 50| is energized from this same positive terminal through a resistance fait and ole-coupled at SI2 by a condenser 5m. The anode of 50| is connected through a condenser 5rd with the positive terminal of dit, and to the cathode of the diode 502, the anode of which is connected directly with the anode of the triode 503 and, through a resist ance 52|, with the positiv-e terminal of 5|3. The output terminals of the apparatus are terminals 522, 523 of the condenser 52B,

The operation is as follows: Control pulses of a suiciently high positive amplitude being apN plied at 506, the control grid of 50| assumes, if

l0 the assembly 5B1-5M has a time constant sufficiently large with respect to the recurrence period of said pulses, an average voltage such that the pulse peak corresponds to a grid voltage close to the cathode potential, while, during the time separating the pulses, the cathode current is zero. In such conditions, the tube 50| is operating in a linear portion of its anode current/suppressor grid characteristic at the time of the peak of the control pulses and a voltage proportional to the instantaneous value of the voltage applied at 50d appears at the terminals 522, 523 of 520. This voltage is stored until such time when 520 is discharged through 5&2 under the action of a rest setting pulse of a negative polarity applied at Erl@ to the grid of 503 through the condenser 505.

When the apparatus is used at the sending end, it is arranged for the control pulse which is obtained from the generator H0, after the delay introduced by a fraction of to occur shortly after the rest setting pulse which is merely the pilot pulse generated by H0. The amplitude of the modulation signal from |0I, |02 or |03 and modified by |04, |05 or |06 is thus measured periodically shortly after the apparition of each pilot pulse and stored at the output terminals of |01, |08 or |09 until the appearance of the next pilot pulse.

When the apparatus is used at the receiving end, no signal is applied to the first input while the second one receives the pulses from the counting selector |253. The charge taken by the ca pacity 525 is then proportional to the duration of the pulses, i. e. finally, to the instantaneous value of the modulation signal.

The operation of a measuring and storing device, at the sending or receiving ends, Will be better understood by an inspection of Figure 6, in which:

Line A represents the diagram. as a function of time, of the pilot pulses applied, in the form of rest setting pulses, to the third input of a sending and measuring and storing device.

Line B represents the diagram, as a function of time, of a modified modulation. signal such as applied to the first input of this sending end measuring and storing device.

Line C shows the diagram. as a function of time, of the control pulses applied to the second input of this sending end measuring and storing device.

Line D shows the diagram, as a function of time, of the signals collected at the output from this sending end measuring and storing device, their magnitude being counted from the upper horizontal line.

Line E shows the diagram, as a function of time, of the pulse groups received at the input to the receiving end of the transmission system. p1; p2; p3 are the pilot pulses. an, am the pulses corresponding to the first communication channel and to the first, second, groups, am, azz the pulses corresponding to the second communication channel, and to the first, second groups, etc.

Line F shows the diagram, as a function of time, of the pulses applied to the second input of the receiving end measuring and storing device |22. In the particular case of this measuring and storing device |22, the duration of these pulses is equal to the time separating the initial condition restoring pulse applied to the selector |20 (pulse from line H, which is also the rest setting pulse of the measuring and storing device |22), of the first channel pulse. In other words,

acsavee the duration of the pulse applied to the second input of |22 is not equal to the time separating the pilot pulse (such as p1, corresponding to :t1 on line F), of the rst channel pulse, but it is clipped by a constant duration equal to that separating the pilot pulse from the initial condition restoring pulse of the selector |20, i. e. equal to the delay introduced by the device |25.

Line G shows the diagram, as a function of time, of the pulses applied to the second input of the receiving end measuring and storing device |23. The duration of these is equal to the time separating the rst channel pulse (such as an) from the second channel pulse (such as azi).

Line H shows the diagram, as a function of time, of the rest setting pulses applied to the third input of the various measuring and storing devices.

Line I shows the diagram, as a function of time, of the electrical voltage obtained at the output from the measuring and storing device |22, the amplitude of which is counted from the upper horizontal line.

Line J shows the diagram, as a function of time, of the electrical Voltage obtained at the output from the measuring and storing device |23, the amplitude of which is counted from the upper horizontal line.

Lines A, B, C, D, of Figure 6 show clearly the operation of the measuring and storing system for the instantaneous amplitudes of the modulation signals at the sending end.

Lines E to J of the same figure show the operation of the receiving system.

The voltage picked up at the output from the measuring and storing devices |22 and |23 is represented by lines I and J of Figure 6, the rest setting pulses represented by line H being delayed with respect to the pilot pulses so that the auX iliary pulses actuating the modulators |25, |21 and |28 do not coincide in time with the rest setting pulses, which would have the eiect of reducing to zero the voltage obtained at the output from the measuring and storing device at the precise moment when it is desired to use it.

Although the present invention has been described, by way of example, with reference t certain particular embodiments. it should be understood that said embodiments may be replaced by others giving an equivalent result and which can easily be imagined by an expert in the art.

What is claimed is:

In a time division multiplex electric pulse communication system including an integer number N of communication channels, each of which transmits a modulation signal consisting of a sig nal voltage varying in time, said system using N interleaved trains of recurrent communication pulses and at least one train of periodic syn* chronization pulses of period T, a communication link having a transmitting end and a receiving end, a transmitting device comprising a pulse generator of a basic frequency generating periodic pulses of period T, a rst delay network fed from said generator and delivering delayed pulses of same said basic frequency, direct-current restorers in number N respectively modifying said modulation signals so as to transform them into unipolar signals. measuring and storing devices in number N for periodically measuring the instantaneous amplitude of each of said modifled modulation signals and storing its measured amplitude as an electric voltage, each of said devices having input and output terminals and being controlled on one hand by control pulses from said generator and on the other hand by delayed pulses from Said rst delay network, means for respectively applying each of said modified modulation signals from each one of said direct-current restorers to input terminals of one corresponding measuring and storing device, a iirst position modulator fed on one hand from the output terminals of a rst of said measuring and storing devices and on the other hand from de layed pulses from said rst delay network, a second position modulator fed on one hand from the output of said first position modulator and on the other hand through a second delay network from the output terminals of a second of said measuring and storing devices, further position modulators associated with each other through further delay networks and with further measuring and storing devices in the same way as said Iirst and second position modulators are associated with said rst and second measuring and storing devices and in sufficient number for allowing utilization of signals from all the N said measuring and storing devices, means for impressing all position modulated pulses irorn ail of said modulators together with non-modulated synchronization pulses derived from said gcnerator upon the sending end of said communication link, means for impressing all the pulses received at the receiving end of said communication link upon said receiving device, said receiving device comprising a synchronization pulse selector segregating the synchronization pulsos from the other received pulses, a counting pulse selector with its input fed from all the received pulses and controlled by control pulses derived from said synchronization pulse selector and delivering at N pairs of output terminals N output signals of constant amplitude and of duratiun respectively proportional to the time intervals separating two successive pulses pertaining to two adjacent trains of received pulses, said counting pulse selector respectively directing each one of said constant amplitude signals towards one of N different circuits selected according to the 'time of occurrence with respect to the synchronizattion pulses of said two successive pulses, a number N of measuring and storing devices cach rcspectively fed at its input terminals from one of said N different circuits and controlled by peri-A odic pulses issued from said synchronisation pulse selector, each said measuring and storing device storing for a predetermined time interval at moet equal to T a voltage proportional to the duration of that one of said constant amplitude signals which is applied to its input terminals and dem livering said voltage at its output terminals, ainplitude modulators in number N respectively fed on one hand from voltage delivered at output terminals of each one of said measuring and storing devices and on another hand from pulses from said synchronization pulse selector, demodulators each respectively fed from the output of one of said amplitude modulators and means for impressing signals from the output of each one of said demodulators upon one of N corresponding utilization circuits.

GASTON XAVIER NEL Forma.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 2,449,467 Goodall Sept. 14, 1948 2,570,010 Staal Oct. 2, 1951 

